Method of producing alkaline earth metal cyanides



Oct. 9, 1945.

L. J. CHRISTMANN ETAL METHOD 0F PRODUCING ALKALINE EARTH METAL .CYANIDES Filed April 24, 1945` kol/7- our CaKC/W,

Ca (CM2. vv/f3 5,470,124??? w/ ry NH3 j INVENTORS a@ www ATTORNEY Patented Oct. 9, 1945 i UNITED sTATEs PATENT oFFicE METHOD oF PRonUcING ALKALINE EARTH i l METAL crANIDEs Ludwig J. Christmann, Yonkers, N. Y., and Alt fred G. Houpt, Stamford, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine Application April 24, 1943, Serial No. 484,378

. s 4 Claims. (C l. 23-79) The present invention relates to the production covered therefrom is substantially free of ammo- --.of alkaline earth metal cyanides, and more parnia before being used to dissolve newly formed ticularly to a method of preparing the cyanide alkaline earth metal cyanides, for the reason that compoundsinasubstantially pure form. the initial discovery has been made that such The alkaline earth metal cyanides are adapted cyanides are less soluble in alcohol containing for a variety of uses. for example, calcium cyanide ammonia than in ammonia-free alcohol.

is a readily available source of hydrocyanic acid A very important object of the invention, therethrough decomposition when exposed to a moist fore, is toprovide a cycle of operations 'from atmosphere. Consequently, the compound is apwhich alkaline earth metal cyanide diammoniates plicable to such uses as fumigation for. the .conl may be recovered for'subsequent treatment to the trol and extermination of insects. Calcium cyacyanides, where the mother liquors `therefrom nide is also utilizedk in the Imining industry. for containing alcohol,l ammonia and residual cyaexample, in processes for the extraction of metals nide are thus 'treated to recover the ammoniafrom their ores.' Barium and strontium cyanides free alcohol for recycle into the process.

are of particular utility as cementation agents in l5 It has been found that the above objects may fused salt baths for case-hardening iron and steel be attained by establishing a cycle of operation articles. y which includes the steps of forming an alcohol The principal object of this invention is to prosolution of an alkaline earth metal cyanide by vide a method whereby the alkaline earth metal treating a mixture of a compound chosen from cyanides may be readily and cheaply obtained. 20 the group consisting of alkaline earth metal ox- Afurther object resides in a method for the proides and hydroxides and an alcohol chosen from duction of thealkallne earth metal cyanides rethe group consisting of methyl and ethyl alcoquiring only simple equipment with' high efiicienhol with hydrocyanic acid, treating the alcohol cies. Other objects will appear hereinafter. solution with ammonia, separating the precipi- AThe prior art teaches that calciumcyanide may tated alkalinev earth metal cyanide diammoniate be formed by reacting .calcium oxide or calcium from the mother liquor, deammoniating the same hydroxide .with hydrocyanic acid in methyl or to produce the desired alkaline earth metal cyaethyl alcohol as a suspending medium. The thus nide and recovering alcohol and/or ammonia for produced calcium cyanide immediately goes into return to the cycle. solution in the alcohol yand may be recovered A convenient method of carrying out the above therefrom by adding an excess amount of hydrocycle of operation is shown in diagrammatic form cyanic acid. in the accompanying ow sheet. When the meth- It is known to these lapplicants that other alkaod is used to produce the cyanide of calcium,

line earth metal cyanides may be similarly formed for example, a methyl alcohol solution of calcium by treating the corresponding oxides or hydroxcyanide is formed by passing gaseous hydrocyanic ides. Y acid into a continuously agitated slurry of cai- It is valso knownin the prior "art that if calcium hydroxide in dry methyl alcohol cooled to a cium hydroxide or calcium oxide is suspended temperature preferably below C. When a in methyl or ethyl alcohol and there is added commercial grade of calcium hydroxide is used, theret hydrocyanic' acid gaS t0 Whihammfmia 40 which may contain impurities such as silica, aluis admixed, that calcium cyanide diammoniate mina, silicates, etc., or should some unreacted will precipitate. calciumhydroxide remain in the menstruum, the

In any commercial method involving the sepinsoluble materials may be removed by filtration, aration of an alkaline earth metal cyanide dithe filter cake washed with methyl alcohol and ammoniate from mother liquors containing meththe washings added to the filtrate.- The alcoyl or ethyl alcohol, the alcohol must be recovhol solution of calcium cyanide is alight strawered or recycled or else the expense involved is colored liquid which is reasonably stable upon such as to be objectionably high. These applistanding, particularly if maintained at low temcants have discovered that one cannot take these peratures.

alcoholic mother liquors and recycle them with- In the preferred form, dry ammonia gas is,

out treatment. g then introduced into the calcium cyanide solu'- The present invention, therefore, is based upon tion, whereupon calciumv cyanide diammoniate is the fact that these alcoholic mother liquors conprecipitated as a crystalline, grayish-white, taining ammonia and residual cyanide must be y readily illterable solid, having a slight pinkish ytreated in such a manner that the alcohol recast. Due`l to the comparatively high heat of solution of ammonia in methyl alcohol, cooling of the mixture during the ammoniation` is desirable, preferably to a temperature below 35 C., to avoid undue azulmic decomposition and darkening of the liquor.

Where anhydrous liquid ammonia is available, this material may be used advantageously for the simples-reason that its addition at this point tends to maintain a, desirably low temperature in the precipitating vessel.

While the use of ammonium hydroxide has a drawback in that it introduces water, yet in the case of concentrated ammonium hydroxide, only small quantities of water would enter the reacting menstruum, which may not cause a sumcient lowering of nal yields to be entirely objectionable.

The slurry of calcium cyanide diammoniate is then filtered and the diammoniate may be washed with methyl alcohol saturated with ammonia. When so washed, the combined illtrate and washings containing methyl alcohol, ammonia and residual calcium cyanide aretreated with a compound which, through double decomposition with the residual calcium cyanide, forms an insoluble calcium compound and a soluble cyanide. Compounds which may be used for this purpose are carbonates, and in4 particular, the alkali metal carbonates, e. g. sodium carbonate, which are added to the mother liquor preferably in aqueous solution. The mixture is then filtered to remove the precipitated calcium carbonate. The filtrate is charged into a stripping still equipped with a fractionating column and a condenser. The alcohol and ammonia pass from the fractlonating column into the condenser where they are separated and separately returned to the cycle. The aqueous cyanide residue is removed from the still and may be used for speclilc purposes known in the art.

In the above step, the mother liquor from the diammoniate precipitation is thus treated for the purpose of having present a more stable cyanide, namely, sodium cyanide, from which the alcohol can be distilled. If the mother liquor is heated to a temperature sufncient to distill olf the alcohol, a reaction takes place between the residual calcium cyanide and the alcohol forming impurities which carry over in the distillate.

'i'he calcium cyanide diammonlate is then deammoniated by heating to produce the substantially pure calcium cyanide, and the evolved ammonia returned to the cycle. A temperature of from 200 to 230 C. is required for rapid separation of the ammonia. Temperatures within the range of 180 to 325 C. are feasible. However, care must be taken at the higher temperatures to avoid decomposition of the calcium cyanide. The deammoniation may be carried out by heating the diammoniate under a partial vacuum to avoid the contact of air and particularly moisture, and to facilitate the removal of the evolved ammonia.

As above stated, a highly important step in the above cycle is the treatment of the mother liquor from the diammoniate precipitation involving the recovery of the alcohol and ammonia reagents. It is important and again emphasized that the recovered alcohol be substantially ammonia-free when returned to the cycle as it has been found that an ammonia content greater than about one percent greatly impedes the dissolution of the calcium cyanide therein. Recycling the mother liquor as such would therefore lessen the elciency of the process. Furthermore, removal of the ammonia by merely heating the mother liquor is unsatisfactory as azulmicdecomposition takes place with .the formation oi' impurities soluble therein which lessen the grade of the ilnal product if this liquor is used in a subsequent extraction cycle. As a consequence, by recovering the cyanide, alcohol and ammonia separately from the mother liquor, interference of one with the other or with the efficient operation or the entire cycle is avoided, while at the same time all va1ues can thus be used in this or other processes.

Example dered calcium hydroxide were suspended in 1,000 cc. of dry methyl alcohol. 2.24 moles of gaseous hydrocyanlc acid were passed slowly into the agltated slurry maintained at a temperature between 15 and 20 C. Agitation of the slurry was continued for l5 minutes after the addition of the hydrocyanic acid. The resulting liquor containing excess calcium hydroxide in suspension was filtered and the lter cake washed with 50 cc. o1' dry methyl alcohol. The combined filtrate and washings were treated with 5 moles ci gaseous ammonia at a temperature of about 20 C. with continuous agitation. The resulting suspension of calcium cyanide diammoniate crystals was iiltered, and the filter cake washed with cold dry methyl alcohol saturated with ammonia. The combined filtrate and wash liquor containing methyl alcohol, ammonia and residual calcium cyanide was treated with a 5% aqueous sodium carbonate solution to convert the calcium cyanide to sodium cyanide. The precipitated calcium carbonate was illtered off and the ltrate charged into a stripping still'equipped with a i'ractonating column and a condenser. The methyl alcohol and ammonia were distilled from the mixture leaving the aqueous sodium cyanide residue in the still. The methyl alcohol was condensed and recovered substantially ammonia-free. The ammonia was subsequently recovered and recycled. The crystalline calcium cyanide diammoniate was heated under a partial vacuum for 4 hours at a temperature oi' from 200 to 220,C., and the evolved ammonia recovered. The remaining product was a pale gray powder, analyzing 97.5% calcium cyanide.

Similarly, other alkaline earth metal cyanides may be prepared in substantially pure form utilizing either the alkaline earth metal oxides or hydroxides, it being highly important that in the recycling of the alcohol, the ammonia be removed.

When ethyl alcohol is used in place of methyl alcohol in the process, a larger quantity will be required due to the lower solubility o1' the alkaline earth metal cyanides therein.

The operation as described, affords a reliable and relatively inexpensive process for producing high grade alkaline earth metal cyanides.

While the inventiony has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

We claim:

1. A method of producing an alkaline earth metal cyanide which includes the steps oi' forming an alcohol solution of an alkaline earth metal cyanide by adding HCN to a mixture oi' a compound chosen from the group consisting of the oxides and hydroxides of the alkaline earth metgrams (1.34 moles) of reagent grade, pow`` v.alsand an alcohol chosenrfrom the group con- Sistinev of methyl and ethyl alcohol adding NH3 to the alcohol solution. separating the precipitated alkaline earth metal cyanide cliammoniatc from the mother liquor containingT alcohol, ammonia and residual alkaline earth metal cyanide, deammoniatina the valkaline earth metal cyanide diarnmoniate, separatingT a substantially ammoniafree alcohol from the mother liquor and returning the said alcohol to the cycle.

2. A method of producing an alkaline earth metal cyanide which includes the steps of forming an alcohol solution of an alkaline earth metal cyanide by addingy HCN to a mixture of a compound. chosen from the group consisting of the oxides and hydroxidesy of the alkaline earth metals and an alcohol chosen from the group consisting of methyl and ethyl alcohol adding NH3 to the alcohol solution, separating the precipitated alkaline earth metal cyanide diammoniatel from the mother liquor containing alcohol, ammonia and residual alkaline earth metal cyanide, deammoniating the alkaline earth metal cyanide diammoniate and returning the ammonia therefrom to the cycle, separating a substantially ammonia-free alcohol from the mother liquor and returning the said alcohol ,to the cycle. A

3. A method of producing an alkaline earth metal cyanide which includes the steps of forming an alcohol solution of an alkaline earth metal cyanide by adding HCN t0 a mixture of a compound chosen from the group consisting of the oxides and hydroxides of the alkaline earth metals and an alcohol chosen from the group consisting of methyl and ethyl alcolici adding NH3 to thc alcohol solution, separating' the precipitated alkali-ne earth metal cyanicu` diaromoniate from the mother liquor containing alcohol, ammonia and residual alkaline cai-th metal cyanide, separating a substantially ammonia-free alcohol from the mother liquor and returning the said alcohol to the cycle, cle-am:noniaine the alkaline earth metal cyanide diammoniatc, recouerinfz the ammonia, from the mother' liquor and the deammoniation step and returning the same to the cycle. Y

4. A method of producintY calcium cyanide which includes the steps of forming a methyl alcohol solution of calcium cyanide by addini,7 HCN to a mixture of calcium hydroxide andmethyl alcohol, adding NH3 to the alcohol solution of calcium cyanide, filtering the precipitated calcium cyanide diammoniate from the mother liquor containing methyl alcohol, ammonia and residual calcium cyanide, adding aqueous sodium` carbonate to the mother liquor' and removing: the precipitated calcium carbonato, distilline the methyl alcohol and ammonia from `the thusY treated mother liquor, recovering the aqueous sodium cyanide from the still residue, separately returning the methyl alcohol and ammonia to the cycle, heating the calcium cyanide diammoniate under partial vacuum at a temperature of from 200 to 220 C. and returning the evolved ammonia to the cycle.

LUDWIG J. CHRISTMANN. ALFRED G. HOUPT. 

